The Physics Beyond Colliders initiative is an exploratory study aimed at exploiting the full scientific potential of the CERN's accelerator complex and scientific infrastructures through projects complementary to the LHC and other possible future colliders. These projects will target fundamental physics questions in modern particle physics.ii 7 Physics reach of PBC projects 66 8 Physics reach of PBC projects in the sub-eV mass range 66 8.1 Axion portal with photon dominance (BC9) 66 9 Physics reach of PBC projects in the MeV-GeV mass range 73 9.1 Vector Portal 78 9.1.1 Minimal Dark Photon model (BC1) 78 9.1.2 Dark Photon decaying to invisible final states (BC2) 83 9.1.3 Milli-charged particles (BC3) 90 9.2 Scalar Portal 93 9.2.1 Dark scalar mixing with the Higgs (BC4 and BC5) 93 9.3 Neutrino Portal 97 9.3.1 Neutrino portal with electron-flavor dominance (BC6) 98 9.3.2 Neutrino portal with muon-flavor dominance (BC7) 101 9.3.3 Neutrino portal with tau-flavor dominance (BC8) 103 9.4 Axion Portal 106 9.4.1 Axion portal with photon-coupling (BC9) 106 9.4.2 Axion portal with fermion-coupling (BC10) 110 9.4.3 Axion portal with gluon-coupling (BC11) 113 10 Physics reach of PBC projects in the multi-TeV mass range 115 10.1 Measurement of EDMs as probe of NP in the multi TeV scale 115 10.2 Experiments sensitive to Flavour Violation 116 10.3 B physics anomalies and BR(K → πνν) 120 11 Conclusions and Outlook 121 A ALPS: prescription for treating the FCNC processes 123 B ALPs: production via π 0 , η, η mixing 126 Executive SummaryThe main goal of this document follows very closely the mandate of the Physics Beyond Colliders (PBC) study group, and is "an exploratory study aimed at exploiting the full scientific potential of CERN's accelerator complex and its scientific infrastructure through projects complementary to the LHC, HL-LHC and other possible future colliders. These projects would target fundamental physics questions that are similar in spirit to those addressed by high-energy colliders, but that require different types of beams and experiments 1 ". Fundamental questions in modern particle physics as the origin of the neutrino masses and oscillations, the nature of Dark Matter and the explanation of the mechanism that drives the baryogenesis are still open today and do require an answer.So far an unambiguous signal of New Physics (NP) from direct searches at the Large Hadron Collider (LHC), indirect searches in flavour physics and direct detection Dark Matter experiments is absent. Moreover, theory provides no clear guidance on the NP scale. This imposes today, more than ever, a broadening of the experimental effort in the quest for NP. We need to explore different ranges of interaction strengths and masses with respect to what is already covered by existing or planned initiatives.Low-mass and very-weakly coupled particles represent an attractive possibility, theoretically and phenomenologically well motivated, but currently poorly explored: a systematic investigation should be pursued in the next decades both at acc...

This Preliminary Design Report is the main deliverable of the Design Study phase period 2011-2014 and served as a reference for the international Cost and Schedule Review called by the CERN Director of Accelerators and Technology in March 2015. Following the very positive results of the reviews, the CERN management endorsed the cost and plan (with some changes mainly related to civil engineering and the financial profile) and the CERN Council approved the project in September 2015 (formal approval for the MTP period 2016-2020, and endorsement of the full Cost-to-Completion until 2026). The project leadership is particularly grateful to the CERN management for its continuous support and encouragement and in particular to the Director-General Rolf Heuer for his personal engagement in having the project initiated and approved during his mandate.

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The new European Strategy for Particle Physics, adopted by the special CERN Council of Brussels on 30 May 2013, placed HL-LHC as a first priority project for the next decade. Consequently, CERN management inserted the project in the Medium Term Plan (5-year plan) and a kick off meeting of HL-LHC as a construction project was organized in Daresbury on 11 November 2013. The HL-LHC project is accompanied by upgrade projects of all LHC Experiments and by the LHC Injector Upgrade Project (LIU). The Experiment upgrade projects are dealt with by their International Collaborations. The LIU project has a separate management, project structure and budget line and plans for a complete implementation during Long Shutdown 2 (LS2), by the end of 2020. The Experiments upgrade and LIU projects are not covered by this TDR.A Cost and Schedule Review series, reviewing both the HL-LHC and LIU projects and reporting to the CERN Director of Accelerators and Technology, Dr. Frédérick Bordry, started in March 2015, with C&SR-I. Following the very positive results of the review, the CERN management endorsed the cost and planning. In September 2015 the CERN Council approved the MTP 2016-2020, containing the funding for the project for that period and envisaging the full Cost-to-Completion (CtC) of the project by 2026. Finally in June 2016, the CERN management had the High Luminosity LHC project, i.e. the upgrade of the collider and its infrastructure, formally approved by the CERN Council, with full financing till 2026. The approved CtC is 950 MCHF of material budget in CERN accounting.In August 2016, a re-baselining of the HL-LHC project was approved by CERN management (and endorsed by the C&SR-II of October 2016) in order to keep the CtC ceiling while accommodating extra cost in the technical infrastructure (mainly in the civil engineering). The present TDR reflects the design of the project at the time of approval by the CERN council, June 2016, with the modifications introduced in the re-baselining exercise in summer 2016.The project leadership is particularly grateful to the CERN management for its continuous support and encouragement and in particular to the CERN Director of Accelerators and Technology, Dr. Frédérick Bordry for his continuous support and guidance from the beginning of the project, to former Director-General Dr. Rolf Heuer for his engagement in having the project initiated and started the funding during his mandate, as well as to the present Director-General Dr. Fabiola Gianotti, for having pursued and obtained the full approval of the entire HL-LHC project by the Council in June 2016, the first CERN project with such status after the LHC.

Heavy Neutral Leptons (HNLs) are hypothetical particles predicted by many extensions of the Standard Model. These particles can, among other things, explain the origin of neutrino masses, generate the observed matter-antimatter asymmetry in the Universe and provide a dark matter candidate. The SHiP experiment will be able to search for HNLs produced in decays of heavy mesons and travelling distances ranging between O(50 m) and tens of kilometers before decaying. We present the sensitivity of the SHiP experiment to a number of HNL's benchmark models and provide a way to calculate the SHiP's sensitivity to HNLs for arbitrary patterns of flavour mixings. The corresponding tools and data files are also made publicly available.